Rad Quality Exam 1

What are photons?

bundles of energy which travel through space at the speed of light

Photons travel through space as __

waves

What are the two components of waves?

1. electric field

2. Magnetic field

What sets photons apart since they all travel at the speed of light?

frequency

Light photons __ divergence the farther away you get

increase

What is rectification?

AC from electrical source is converted into DC

takes negative component of the input voltage to positive voltage then converts to DC

What is mAs?

quantity of electrons

What is kVp?

x-ray energy and quality

What is thermionic emission?

high heat causing outer electrons to be released

Where does thermionic emission take place?

inside x-ray tube on cathode filament

After thermionic emission, what happens next?

space charge effect→ accumulation of electrons around the filament before high voltage is applied to tube circuit

What are the two components of the cathode?

1. Tungsten filament→ small focal spot for extremities and large focal spot for central axis anatomy

2. Focusing cup→ nickel (negatively charged and helps accelerate electrons forward

When is potential energy converted into kinetic energy?

when pushing the exposure button

Potential energy is set by the __ across the tube

kVp

Once energy slams against the anode, what happens?

99% of electrons convert into heat

1% converts into x-rays

What is the anode made of ?

tungsten (Z=74)

Why do anodes rotate?

dissipate heat

What is Bremsstrahlung radiation?

85% of interactions (MC anode interaction) when kVp is above 70

braking radiation

if below 70 kVp, accounts for 100% of interactions

bombarding electron interacts with whole atom

large range of energies

What is characteristic radiation?

15% of interactions when kVp is above 70

if less than 70 kVp, not produced

inner shell electron interaction

inner shell binding energy of tungsten is 69.5keV

radiation released is of a specific energy

Increasing kVp causes an increase in the maximum photon energy and therefore __ the number of photons produced

increases

How does frequency of photon determine its energy?

high frequency→ more likely to pass through or interact with patient

lower frequency→ more likely to absorb in patient

What does beam quality control?

controls kVp

controls contrast

What does beam quantity control?

controlled by mAs

controls the density

What happens once x-ray shoots toward patient?

attenuation

What is attenuation?

reduction in intensity of the beam as it passes through matter (patient)

What are the three patient interactions with x-ray?

1. Absorbed

2. Scattered

3. Transmitted

What determines attenuation/transmission?

1. Tissue thickness

2. Tissue density

3. atomic number

4. photon energy→ MOST controllable factor

What is a radiograph?

visual record of x-ray attenuation and transmission

What are the 5 radiographic densities? (low density/transmission to high density/absorption)

1. Air

2. Fat

3. Water

4. Bone

5. Metal

What is radiolucent vs radiopaque?

Radiolucent→black areas

Radiopaque→white areas

more atoms and larger atoms= __

more interactions=more absorption=whiter

Photoelectric effect increases with __

1. Higher atomic number

2. increasing mass density

3. lower x-ray beam energies→kVp decreases

4. high atomic number structures→ causes absorption

EX: bone and metal

What is photoelectric effect?

10% of interactions

photon is absorbed

lots of black and white (contrast)

What is compton scatter?

MC interaction (90%)

deflects photon

increases with higher energy as kVp increases

a lot of grey

What increases compton scatter?

1. increases mass density

2. increasing electron density

3. higher x-ray beam energies

4. low density structures→ water, air, soft tissue

What affects our exposure settings?

1. Collimation

2. Patient size and position

3. SID→ less mAs or kVp is required for 40”

4. Grid usage →grid requires more mAs

5. Contrast→ requires higher kVp for soft tissue

What is collimation?

using lead shutters to increases or decrease the number of x-rays used

trims/crops the x-ray beam so that you only x-ray the area you want in the iamge

If you want high contrast (black and white), what should your kVp be?

low kVp

If you want low contrast (gray), then what kVp do you want?

high kVp

_ increase the penetrating power of x-ray beam and results in less absorption and more scatter

higher kVp

What gives more grays?

increased transmission and compton scatter normally due to higher kVp

__ decreases the x-ray beam penetration resulting in more absorption and less scatter

lower kVp

What increases photoelectric interactions which contributes to fewer shades of gray?

lower kVp

An unwanted layer of radiation is referred to as __

noise or fog

As kVp is reduced, average photon energy is reduced which allows photoelectic interactions to_ and scatter events to_

increase

decrease

A 15% increase in KVP has the same effect as __ the MAS

doubling

A 15% decrease in KVP has the same effect as _ the MAS by half

decreasing

What is the primary controller of quality?

kVp

kVp can change __ and _

contrast and density

T/F KVP should be changed in small increments

true

Beam quantity is often referred to as __

image density

What is mAs?

quantity of x-rays produced

Image density refers to the __ of the image

blackness

Darker areas are __ dense (high)= more x ray exposure

more

Lighter areas=_ density (low)=less x-ray exposure

less

Image density reflects __

number of photons that make it to the imaging receptor

As you increase the mAs, the amount of ionizing radiation __

increases

What is exposure time?

how long the x-rays are being produced for

T/F High mAs and low exposure time is preferred

true

If you double the SID, what happens to intensity of radiation?

decrease by a factor of 4

What is SID?

source to image distance

40”→ magnifies anatomy (increase divergence)

72”→decreases magnification of anatomy (decreased divergence)

Inverse square law states that as you move the x-ray tube back, you need to __ your mAs

increase

What will be the first thing to become overexposed if you use too many x-rays?

fat

What will the first thing to become underexposed be?

bone

The minimum change needed to correct for density is a factor of _

2

Overexposed images will have a distinct lack of quantum mottle while appearing __

saturated or burnt out

What is quantum mottle?

graininess on an underexposed image

If people always turn the mAs up, the images will always turn out __

mAs creep→ increasing radiation dose

What is used to avoid mAs creep? (TQ)

exposure index

What is exposure index dependent on?

1. collimation

2. central ray

What is fluroscopy?

moving x-rays (real time radiography)

What is used for a GI contrast study?

barium→ high attenuation

What is OID?

object to image distance

Increased OID will __

increase magnification and penumbra

Decreased OID __

reduced magnification

What is penumbra?

distortion and blurring that comes with increased OID

What is DEXA?

two different x-ray energy beams and compares how much is transmitted at each

small amounts of radiation

DEXA bone denstiy testing is best standardized method available to diagnose_

osteoporosis

What is a T-score?

amount of bone you have compared with a young adult of the same gender with peak bone mass

What is a Z score?

amount of bone you have compared with other people in your age group and of the same size and gender

A T score of less than -2.5 and below is defined as __

osteoporosis (highest fracture risk)

What does a whole body DEXA assess?

1. Total fat mass and percentage

2. lean body mass

3. visceral adipose tissue

4. fat mas index

5. bone mineral density

What is a CT?

measuring how much of the X-ray beam is transmitted at many angles around the patient

3d mapping of different areas of body

CT uses __ units

hounsfield

X-rays travel in __ and then diverge

straight lines

Increasing collimation will __ the x-ray beam

reduce

light field gets smaller

Decreasing collimation will __ the x-ray beam

increase

light field gets bigger

What will increased collimation all do?

1. decrease patient dose

2. decrease scatter production

3. increase image contrast

4. decrease intensity of beam

Why is PA chest the best position to review the cardiac shadow?

see the true size of the heart

Geometric unsharpness is referred to as __

penumbra

What is a grid?

thin plate in the front of the Bucky that has thin strips of lead that stops scattered x-rays from reaching the film

cleans up scatter

What is the recommended grid ration? (TQ)

12:1

What are the two types of grids?

1. parellel

2. focused

A-P view requires patients back to be toward __

image receptor

P-A requires patient’s front to be towards__

imaging receptor

Left lateral requires patient’s __ toward IR

left side

Right lateral has patient’s __ toward IR

right side

Oblique view requires a __ angle

45 degree

Measure part thickness to help determine __

mAs necessary

More patient mass will increase _ and decrease _

scatter

transmission